1. Field of the Invention
The present invention relates to a watercraft control method and a watercraft control system.
2. Description of the Related Art
As described in Japan Laid-open Patent Application Publication No. 2010-203416, keeping constant the rotation speed of an engine has been conventionally performed as a control to keep constant the velocity of a watercraft. By thus keeping constant the engine rotation speed highly related to the vessel velocity, the vessel velocity can be controlled to fall in a predetermined range.
However, even when the engine rotation speed is kept constant, the vessel velocity varies inevitably due to influence of waves, the tide, the wind and so forth or depending on whether or not a hydroplaning state is produced. Therefore, it is desirable to directly detect and control the vessel velocity so as to enhance as much as possible accuracy in keeping the vessel velocity constant.
For example, when the vessel velocity is accurately detectable by position measuring means such as a GPS function, the vessel velocity can be accurately kept constant by a feedback control to regulate a thrust in accordance with a difference between a target vessel velocity and an actual vessel velocity.
However, chances are that even when the feedback control is performed, a temporal decrease in vessel velocity is caused in, for instance, turning of the watercraft. For example, when the watercraft tows a water skier in a towing mode, a temporal decrease in vessel velocity may affect a hydroplaning state of the water skier.
Incidentally, when the actual vessel velocity deviates from the target vessel velocity under the feedback control, the actual vessel velocity can be automatically restored to the target vessel velocity. However, in increasing or decreasing the vessel velocity in a specific region, it is required to perform an additional action of deactivating an automatic cruise control and switching into a manual cruise control in the specific region.